[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 182357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE AUG 18 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2330 UTC.

...SPECIAL FEATURES...
THE CENTER OF HURRICANE BILL AT 2100 UTC WAS LOCATED BY AN AIR
FORCE RESERVE HURRICANE HUNTER AIRCRAFT NEAR 16.6N 52.2W OR
ABOUT 635 MILES...1025 KM...EAST OF THE LEEWARD ISLANDS. BILL IS
MOVING TOWARD THE WEST-NORTHWEST OR 290 DEGREES AT 14 KT. THE
ESTIMATED MINIMUM CENTRAL PRESSURE IS 962 MB WITH MAXIMUM
SUSTAINED WIND SPEEDS OF 95 KT WITH GUSTS UP TO 110 KT MAKING
BILL A STRONG CATEGORY 2 HURRICANE ON THE SAFFIR-SIMPSON SCALE.
HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75
KM...FROM THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND
OUTWARD UP TO 175 MILES...280 KM. WEST-NORTHWEST MOTION IS
EXPECTED TO CONTINUE TONIGHT...FOLLOWED BY A TURN TOWARD THE
NORTHWEST ON WEDNESDAY. STRENGTHENING IS FORECAST DURING THE
NEXT 48 HRS AND BILL IS EXPECTED TO BECOME A MAJOR HURRICANE
LATER TONIGHT OR WEDNESDAY. PLEASE READ
THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
TCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION
SURROUNDS THE CENTER OF BILL AND IS FROM 13N-18N BETWEEN 50W-55W.

...TROPICAL WAVES...
A TROPICAL WAVE EXTENDS FROM 16N38W TO 8N34W MOVING W NEAR 15
KT. THE WAVE IS AHEAD OF A DEEP LAYER MOISTURE MAXIMUM OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY. THE MOISTURE IS BEING DRAWN
INTO THE CIRCULATION OF HURRICANE BILL WHICH EXPLAINS THE TILTED
AXIS OF THE WAVE. THE WAVE ALSO LEADS A DRY SAHARAN AIR LAYER
WHICH IS INHIBITING ANY DEEP CONVECTION NEAR THE WAVE.
HOWEVER...ISOLATED SHOWERS ARE FROM 6N-9N BETWEEN 33W-37W AND
FROM 14N-16N BETWEEN 34W-37W.

A TROPICAL WAVE IS ALONG 77W S OF 21N MOVING W NEAR 25 KT. THIS
WAVE ORIGINATED AS THE REMNANTS OF ANA THAT DISSIPATED
YESTERDAY. WHILE THERE IS A LOW PROBABILITY OF
REGENERATION...SHOWERS/THUNDERSTORMS ARE AFFECTING A LARGE AREA
INCLUDING CUBA...THE BAHAMAS AND S FLORIDA. NUMEROUS
MODERATE/SCATTERED STRONG CONVECTION IS FROM 18N-27N BETWEEN
75W-80W. THIS ACTIVITY IS ENHANCED BY UPPER LEVEL DIFFLUENCE.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 12N16W 10N25W 11N33W 9N39W
12N46W 10N62W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS
FROM 11N-15N BETWEEN 17W-22W. SCATTERED MODERATE CONVECTION IS
FROM 7N-10N BETWEEN 21W-26W.
...DISCUSSION...

THE GULF OF MEXICO...
THE GULF OF MEXICO IS WET TONIGHT AS SHOWERS/THUNDERSTORMS
ARE ACROSS MUCH OF THE BASIN. SCATTERED SHOWERS/THUNDERSTORMS N
OF 29N BETWEEN 85W-97W ALONG THE COASTLINE OF THE GULF STATES
ARE ENHANCED BY SURFACE CONVERGENCE NEAR A TROUGH N OF THE
DISCUSSION AREA ACROSS LOUISIANA AS WELL AS UPPER LEVEL
DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE ACROSS THE GULF OF
MEXICO CENTERED NEAR 27N90W AND AN UPPER LEVEL TROUGH ACROSS THE
CENTRAL UNITED STATES. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER
HIGH AND AN UPPER LEVEL LOW OVER CENTRAL MEXICO NEAR 23N102W IS
SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ALONG THE E COAST OF
MEXICO FROM 21N-24N BETWEEN 95W-98W. UPPER LEVEL DIFFLUENCE
BETWEEN THE UPPER HIGH AND ANOTHER UPPER LEVEL LOW S OF CUBA
NEAR 20N80W IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS
THE YUCATAN PENINSULA AND THE ADJACENT COASTAL WATERS IN THE BAY
OF CAMPECHE. SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE W
COAST OF FLORIDA FROM 25N-30N BETWEEN 81W-84W ENHANCED BY UPPER
LEVEL DIFFLUENCE BETWEEN THE UPPER HIGH AND AN UPPER LEVEL
TROUGH OVER THE NW ATLC. FINALLY...ISOLATED
SHOWERS/THUNDERSTORMS ARE ACROSS THE CENTRAL GULF FROM 23N-28N
BETWEEN 86W-91W. EXPECT SHOWERS/THUNDERSTORMS TO CONTINUE ACROSS
THE GULF AS THE TROPICAL WAVE ALONG 77W...REMNANTS OF ANA...MOVE
WWD.

THE CARIBBEAN SEA...
ISOLATED SHOWERS/THUNDERSTORMS ARE ACROSS THE FAR NW CARIBBEAN N
OF 17N BETWEEN 81W-86W. THIS ACTIVITY IS ENHANCED BY UPPER LEVEL
DIFFLUENCE BETWEEN AN UPPER LEVEL LOW S OF CUBA NEAR 20N80W AND
AN UPPER LEVEL RIDGE THAT DOMINATES THE GULF OF MEXICO. UPPER
LEVEL DIFFLUENCE BETWEEN THE UPPER LOW AND AN UPPER LEVEL HIGH E
OF THE BAHAMAS NEAR 25N70W IS ENHANCING NUMEROUS
SHOWERS/THUNDERSTORMS ACROSS E CUBA N OF 18N BETWEEN 75W-80W.
THIS ACTIVITY IS ALSO ENHANCED BY SURFACE CONVERGENCE NEAR THE
TROPICAL WAVE ALONG 77W...PREVIOUSLY THE REMNANTS OF ANA.
ISOLATED SHOWERS/THUNDERSTORMS ARE IN THE SW CARIBBEAN S OF 12N
BETWEEN 73W-81W ENHANCED BY THE S PORTION OF THE TROPICAL WAVE
AS WELL AS THE E PACIFIC ITCZ. ELSEWHERE ACROSS THE
CARIBBEAN...DRY AIR ASSOCIATED WITH A SAHARAN AIR LAYER E OF 68W
AND SUBSIDENCE ALOFT ARE SUPPORTING GENERALLY FAIR WEATHER.
EXPECT SHOWERS/THUNDERSTORMS TO CONTINUE ACROSS THE NW CARIBBEAN
AS THE TROPICAL WAVE...REMNANTS OF ANA...MOVE WWD.

THE ATLANTIC OCEAN...
NUMEROUS SHOWERS/THUNDERSTORMS ARE ACROSS THE SW N ATLC FROM
21N-28N BETWEEN 75W-81W...INCLUDING THE BAHAMAS AND S FLORIDA.
THIS ACTIVITY IS ENHANCED BY SURFACE CONVERGENCE NEAR THE
TROPICAL WAVE ALONG 77W...AND A SURFACE TROUGH EXTENDING FROM
24N80W TO 27N76W ACROSS THE NW BAHAMAS. THIS ACTIVITY IS ALSO
ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL LOW S
OF CUBA NEAR 20N80W AND AN UPPER LEVEL HIGH E OF THE BAHAMAS
NEAR 25N70W. UPPER LEVEL DIFFLUENCE BETWEEN THIS UPPER HIGH AND
AN UPPER LEVEL TROUGH N OF 30N WITH AXIS ALONG 75W IS ENHANCING
SCATTERED SHOWERS/THUNDERSTORMS FROM 27N-30N BETWEEN 67W-70W. A
COLD FRONT DIPS INTO THE CENTRAL ATLC NEAR 32N44W EXTENDING TO
28N54W. NO SHOWER ACTIVITY IS CURRENTLY ASSOCIATED WITH THE
FRONT. ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE
DOMINATES ANCHORED BY A 1023 MB HIGH NEAR 34N74W...A 1022 MB
HIGH NEAR 33N61W...AND ANOTHER 1022 MB HIGH NEAR 32N31W. IN THE
UPPER LEVELS...AN UPPER LEVEL TROUGH IS BETWEEN 36W-62W N OF
29N...AND AN UPPER LEVEL HIGH IS CENTERED NEAR 30N30W DOMINATING
THE E ATLC. ACROSS THE TROPICAL ATLC...A BROAD UPPER LEVEL HIGH
IS CENTERED NEAR 20N30W ENHANCING CONVECTION ALONG THE ITCZ NEAR
THE AFRICA COAST.

$$
WALTON







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